It was the second most deadly eruption in the 20th century after the 1902 eruption of Mont Pelee on the Caribbean island of Martinique which killed 29,000 people.

Following the 1985 eruption, Nevado del Ruiz remained active for several more years, culminating in eruptions in 1991 and 1992.

It was not the first time the volcano had caused deaths.

In 1595, 636 people were killed after a mudflow swept down the mountainside. Another eruption in 1845 led to 1,000 deaths.

Around 50 years later settlers began to build the city of Armero directly on top of the hardened mudflow deposits.
After the 1985 disaster the government declared the site of the buried city to be "holy ground".